We may earn a commission when you buy through our links, at no extra cost to you. As an Amazon Associate we earn from qualifying purchases. How we make money
At a Glance
- Overall Collagen supplements were well tolerated in skin trials, with few adverse events reported12.
- Allergy Fish collagen can be a problem if you have a fish allergy; bovine gelatin allergy has also been reported67.
- Kidney stones Gelatin raised urinary oxalate in one small study but not in another45.
- Add-ins High-dose biotin in some collagen blends can skew blood test results8.
- Top pick NAKED Collagen – the #1 pick in our guide to the best collagen powder: one ingredient, bovine collagen peptides, with the NSF Contents Certified mark.
The Short Answer: For most healthy adults, collagen peptides appear to have few side effects. Reviews of randomized trials found collagen generally well tolerated, with a low rate of adverse events12. Most trials were short, though, so long-term safety data are limited.
On this page
The real risks depend on you and the product: fish allergy with marine collagen, a history of kidney stones, and extra ingredients such as high-dose biotin. Supplements aren’t approved by the FDA before they’re sold9, so choosing a product with independent testing matters. For the basics, see our guide to collagen peptides.
Collagen Side Effects at a Glance
| Possible side effect | What the research shows | Who should be careful |
|---|---|---|
| General side effects | Low rate of adverse events in skin trials12 | Most healthy adults are unlikely to have problems |
| Digestive symptoms | No clear signal in trials; one open-label study reported less bloating23 | Anyone who notices fullness or stomach upset |
| Allergic reactions | Fish gelatin antibodies in some people with fish allergy6 | People with fish or beef allergies |
| Kidney stones | Higher urinary oxalate with 30 g of gelatin in one study, no change in another45 | People with a history of oxalate kidney stones |
| Lab test errors | Biotin add-ins interfered with some blood tests8 | Anyone using collagen with high-dose biotin |
| Incomplete protein | Collagen lacks tryptophan10 | People using collagen to replace other protein |
Common Side Effects in Trials
In a 2019 review of 11 randomized controlled trials with 805 people, collagen supplements of 2.5 to 10 g a day for up to 24 weeks were described as generally safe, with no reported adverse events1. A larger 2026 review of 25 randomized trials also found collagen generally well tolerated, with a low incidence of adverse events2.
There are two limits to keep in mind. Trials in the 2019 review lasted 4 to 24 weeks1, and the 2026 review rated most of them as having a high risk of bias2. So collagen looks low risk in the short term, but we can’t say much about years of use.
Digestive Side Effects
We didn’t find trials showing collagen causes bloating or stomach upset more often than placebo. In fact, in one open-label study of women taking 20 g of collagen peptides a day for 8 weeks, 13 of the 14 women who finished reported fewer digestive symptoms, including bloating3. Only 14 of 40 participants completed the study, there was no placebo group, and the authors had ties to the collagen maker3.
If collagen does upset your stomach, try a smaller dose or stop taking it.
Allergic Reactions
Allergy is the clearest safety concern, and it depends on the source:
- Marine collagen: In children with fish allergy, 3 of 10 had antibodies to fish gelatin6. Washing fish skin during gelatin production removed most of the main fish allergen, parvalbumin7, but if you have a fish allergy, ask your allergist before trying marine collagen.
- Bovine collagen: Allergies to bovine gelatin have been reported, for example in children who reacted to vaccines containing it6.
Always check the label for the source. For a side-by-side look at fish and cow collagen, see our guide to marine vs bovine collagen.
Can Collagen Cause Kidney Stones?
Collagen is rich in hydroxyproline, which the body can turn into oxalate, a building block of calcium oxalate kidney stones4. In a 2006 study, eating 30 g of gelatin a day on a controlled diet raised urinary oxalate by 43% compared with whey protein, and doses of 5 to 10 g also raised urinary oxalate4. But in a 2019 study of 5 healthy men, 30 g of gelatin a day for 3 days didn’t change oxalate excretion5.
Neither study measured actual kidney stones. If you’ve had calcium oxalate stones, talk to your doctor before taking collagen, especially at higher doses.
Ingredients in Collagen Blends That Can Cause Problems
Many collagen products aren’t just collagen. Extra ingredients can matter more than the collagen itself:
- Biotin: In a study of 6 healthy adults, 10 mg of biotin a day for 7 days caused interference in 9 of 23 biotin-based lab tests, with some results falsely high and others falsely low8. If your collagen contains biotin, tell your doctor before blood tests. See our guide to biotin and collagen supplements.
- Long ingredient lists: Blends with many added vitamins, herbs or proprietary mixes are harder to judge. A single-ingredient collagen powder is the simplest choice.
Who Should Avoid Collagen or Ask a Doctor First
- People with fish allergy: Avoid marine collagen or ask your allergist6.
- People with a history of kidney stones: Ask your doctor first4.
- People who are pregnant or breastfeeding: We didn’t find trials testing collagen supplements in pregnancy, so ask your doctor.
- Vegetarians and vegans: Collagen comes from animals. See our guide to vegan collagen.
- People relying on collagen for protein: Collagen lacks tryptophan, so it’s an incomplete protein and shouldn’t replace other protein sources10.
How to Lower Your Risk
- Check the source: Fish, cow, pig or chicken, especially if you have food allergies.
- Look for independent testing: The FDA doesn’t approve supplements before they reach the market9, so marks such as NSF help confirm what’s in the tub.
- Read the full label: Watch for high-dose biotin and long proprietary blends.
- Stick to studied doses: Many trials used 2.5 to 10 g a day1.
For what collagen can and can’t do, see our guide to collagen benefits.
Our Top Collagen Pick
1 ingredientNSF Contents Certified9.5 g per serving
The #1 pick in our guide to the best collagen powder. It lists only bovine collagen peptides, so there are no added vitamins, herbs or fish to check for, and it carries the NSF Contents Certified mark.
Final Verdict
Collagen supplements appear to have few side effects for most healthy adults in short-term trials12. The main concerns are allergy to the source (especially fish), a possible rise in urinary oxalate for people prone to kidney stones, and extra ingredients such as high-dose biotin468. Long-term safety data are limited.
If you want to keep it simple, consider NAKED Collagen, a single-ingredient bovine collagen powder with the NSF Contents Certified mark. Compare all picks in our guide to the best collagen powder.
Important: This guide is for general information and isn’t medical advice. Talk to your doctor before taking collagen if you have a food allergy, a history of kidney stones, are pregnant or breastfeeding, or take prescription medicine.
Frequently Asked Questions
What are the side effects of collagen?
What are the side effects of collagen peptides?
Can collagen cause bloating?
We didn’t find trials showing collagen causes bloating more than placebo. One small open-label study reported less bloating with 20 g a day3.
Can collagen cause kidney stones?
Who should not take collagen?
People with fish allergy should avoid marine collagen or ask their allergist first6. People with kidney stones, or who are pregnant or breastfeeding, should ask a doctor first.
Is it safe to take collagen every day?
Daily doses of 2.5 to 10 g for up to 24 weeks were well tolerated in trials1, but long-term data are limited.
Can collagen affect blood tests?
Collagen itself isn’t known to, but biotin added to some collagen products can interfere with certain lab tests8.
Sources & History
References
- Oral Collagen Supplementation: A Systematic Review of Dermatological Applications — Journal of Drugs in Dermatology, 2019
- Efficacy and Safety of Hydrolyzed Collagen Supplementation on Skin Health Outcomes: A Systematic Literature Review of Randomized Controlled Trials — European Journal of Clinical Nutrition, 2026
- Effect of a Daily Collagen Peptide Supplement on Digestive Symptoms in Healthy Women: 2-Phase Mixed Methods Study — JMIR Formative Research, 2022
- Hydroxyproline Ingestion and Urinary Oxalate and Glycolate Excretion — Kidney International, 2006
- Theoretical and Laboratory Investigations of the Effects of Hydroxyproline Ingestion on the Metabolic and Physicochemical Risk Factors for Calcium Oxalate Kidney Stone Formation in a Small Group of Healthy Subjects — International Urology and Nephrology, 2019
- IgE Antibody to Fish Gelatin (Type I Collagen) in Patients With Fish Allergy — Journal of Allergy and Clinical Immunology, 2000
- Parvalbumin in Fish Skin-Derived Gelatin: Is There a Risk for Fish Allergic Consumers? — Food Additives & Contaminants, 2012
- Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults — JAMA, 2017
- Questions and Answers on Dietary Supplements — U.S. Food and Drug Administration
- Significant Amounts of Functional Collagen Peptides Can Be Incorporated in the Diet While Maintaining Indispensable Amino Acid Balance — Nutrients, 2019
Update history
- New guide on collagen side effects covering adverse events in randomized trials, digestive symptoms, fish and bovine allergy, kidney stone risk from hydroxyproline, biotin and other add-ins, who should avoid collagen and how to lower your risk.
